1. Field of the Invention
The present invention relates to medical apparatus, and in particular to a cannula attachment which locks and seals a cannula to a mating syringe port or vacuum device quickly and reliably.
2. Description of Related Art
It is well known in the art to mount a cannula needle to a syringe for withdrawing or injecting fluids into a patient. A typical syringe comprises a cylindrical barrel which serves as a reservoir for the fluids, and a plunger which forces fluid out of the barrel or draws fluid into the barrel similar to a piston and rod assembly. In the case of fluid withdrawal or injection, a needle or cannula is connected to the syringe barrel and inserted into a patient. When withdrawing fluid from a patient, a vacuum is created in the barrel as the plunger is withdrawn, and the vacuum is transferred along a channel in the cannula to its end located at a predetermined location within the body. The fluid surrounding an opening at the end of the cannula is then drawn into the channel and into the barrel of the syringe.
A procedure which utilizes this technique is lipectomy, which involves the removal of excess fat in the layer between the epidermis and the adjacent muscle tissue. Lipectomy can be performed dry, where no fluid is initially injected into the area before the removal of the fat. However, the preferred procedure today is to use a wet technique whereby a fluid including a local anesthetic with vasoconstrictors is injected into the area, which is known to reduce postoperative pain and blood loss. In either event, a long cannula with preferably a blunt tip is used to withdraw the fat so as to limit the number of incisions in the body. The cannula is connected to either a syringe or a machine used for suction. Although for simplicity a syringe assembly is described, it is to be understood that at all times the use of a machine can be interchanged for a syringe, without deviation from the scope of the invention. The process involves manipulating the cannula back and forth, sometimes vigorously, in order to separate the fat from the attached tissue. Both the vigorous movement and the length of the cannula generate large forces which are transmitted to the connection point of the cannula with the syringe.
It is preferred to use a removable connection between the syringe and the cannula, such that the syringe can be evacuated or replaced while the cannula is in place. Various techniques have been attempted to reliably secure the cannula to the syringe which also permits quick and easy removal of the syringe from the cannula. Johnson, U.S. Pat. No. 5,002,538 discloses an adapter which is designed to mate with a syringe end such that the syringe port, shoulder, and part of the syringe barrel fit into the adapter. The adapter press-fits over the syringe using precise tolerances which purport to lock the syringe into the adapter. However, it is sometimes difficult to achieve the precise tolerances required, especially when working with plastics as is the case with most syringes. The Johnson design is also susceptible to inadvertent displacement by a withdrawing longitudinal force, which can uncouple the pressfit connection. Furthermore, the Johnson adapter covers the end of the syringe preventing a view of the withdrawn fluid until the plunger has been displaced almost a syringe diameter's distance. This is significant, because a higher blood content in the withdrawn fluid signifies that the procedure is complete, and this is determined by visually inspecting the fluid.
The prior art lacks a cannula connection which is reliable and easy to remove and install. The ideal connection would permit a clear view of the syringe barrel and secure the cannula from forces in all directions. Moreover, the connection should provide a fluid tight seal to prevent blood or other bodily fluids from leaking or escaping from the syringe.